piperidines and pyrroline

Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, such as the Pudovik, Arbuzov and Horner-Wadsworth-Emmons (HWE) reactions. The reaction of paramagnetic a-bromoketone produced a vinylphosphonate in the Perkow reaction. Paramagnetic a-hydroxyphosphonates could be subjected to oxidation, elimination and substitution reactions to produce various paramagnetic phosphonates. The synthesized paramagnetic phosphonates proved to be useful synthetic building blocks for carbon-carbon bond-forming reactions in the Horner-Wadsworth-Emmons olefination reactions. The unsaturated compounds achieved could be transformed into various substituted pyrroline nitroxides, proxyl nitroxides and paramagnetic polyaromatics. The Trolox

Topics: Alkenes; Carbon; Molecular Structure; Nitrogen Oxides; Organophosphonates; Piperidines; Pyrroles; Stereoisomerism

2-Aryltetrahydropyridines formed by anionic cyclization or ring-closing metathesis were converted to their N'-aryl urea derivatives. Depending on the position of the unsaturation within the tetrahydropyridine ring, metalation by deprotonative lithiation or carbolithiation led to migration of the N'-aryl substituent to the 2- or 6-position via intramolecular nucleophilic attack of a benzylic organolithium on the aryl ring. The products are a range of 2,2-, 2,2,3-, and 2,6-polysubstituted piperidine derivatives. Related chemistry was observed in pyrroline homologues.

Topics: Cyclization; Lithium; Molecular Structure; Piperidines; Pyridines; Pyrroles; Urea

Design of the new spin-labeled cyclodextrins can significantly extend the functionality of nitroxides. A series of new complexes based on fully methylated cyclodextrin (TRIMEB) covalently bound to the piperidine, pyrroline, pyrrolidine, and pH-sensitive imidazoline type nitroxides has been synthesized and studied using pulse and continuous wave electron paramagnetic resonance (EPR). The influence of the radical and linker properties on the structure of complexes formed has been investigated. Using the electron spin echo envelope modulation technique, we have analyzed quantitatively the accessibility of radicals to solvent molecules in studied complexes depending on the structure and length of the linkers. In all studied systems we observed different types of equilibria between conformations with radical fragment being outside the TRIMEB cavity and radical fragment capping the cavity of TRIMEB. The observed guest-induced shift of equilibrium toward the complex with radical capping TRIMEB cavity was explained by a change of macrocyclic configuration of TRIMEB. Complex with the -NH-CO- linker has been found most perspective for the applications requiring close location of nitroxide to the inclusion complex of TRIMEB. Using continuous wave EPR, we have shown that the pH-sensitive radical covalently bound to TRIMEB maintains its pH-sensitivity, but this complexation does not reduce radical reduction rate in the reaction with ascorbic acid.

Topics: Cyclodextrins; Electron Spin Resonance Spectroscopy; Hydrogen-Ion Concentration; Kinetics; Nitrogen Oxides; Piperidines; Pyrroles; Pyrrolidines; Spin Labels

The efficiency of Overhauser dynamic nuclear polarization (DNP) depends on the local dynamics modulating the dipolar coupling between the two interacting spins. By attaching nitroxide based spin labels to molecules and by measuring the (1)H DNP response of solvent water, information about the local hydration dynamics near the spin label can be obtained. However, there are two commonly used types of nitroxide ring structures; a pyrroline based and a piperidine based molecule. It is important to know when comparing different experiments, whether changes in DNP enhancements are due to changes in local hydration dynamics or because of the different spin label structures. In this study we investigate the key parameters affecting DNP signal enhancements for 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl, a 5-membered ring nitroxide radical, and for 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy, a 6-membered ring nitroxide radical. Using X-Band DNP, field cycling relaxometry, and molecular dynamics simulations, we conclude that the key parameters affecting the DNP amplitude of the (1)H signal of water to be equal when using either nitroxide. Thus, experiments measuring hydration dynamics using either type of spin labels may be compared.

Topics: Computer Simulation; Electron Spin Resonance Spectroscopy; Free Radicals; Indicators and Reagents; Models, Molecular; Nitrogen Oxides; Piperidines; Protons; Pyrroles; Reactive Nitrogen Species; Spin Labels; Water